Method of reclaiming used metal molds



March 9, 1948. I c, T|N$LEY 2,437,626

METHOD OF RECLAIMING. USED METAL HOLDS Filed Sept. 4, 1943 501g. 1 I la luvs/V70 Ba 6. aliffafdfizi'hslgy. wl-rlvs'ss nrram w: r

Patented Mar. 9, 1948 METHOD or aacmnumo USED METAL MOLDS Clifford It. Tinsley, Beverly, N. J., asslgnor to United States Pipe and Foundry Company, a corporation of New Jersey Application September 4, 1943, Serial No. 501,333

The invention relates to a method of reclaiming used metal molds, and is directed specifically to an improvement in procedure for reclaiming steel molds employed in centrifugally casting iron pipe and the like.

Such molds are usually made of forged steel or steel alloys, are of generally cylindrical shape with a wall thickness varying from one and one quarter inches to two inches, and when they are originally manufactured they are bored to the minimum diameter which is permissible for casting pipe having a certain internal diameter. As a result of the high temperatures to which they are subjected when in use, the inner surface of such molds becomes pitted, rough and uneven. Fissures or cracks also develop in the inner surfaces of such molds by reason of the extreme temperature variations to which the molds are subjected during the casting operations, such fissures extending both circumferentially and longitudinally on the inner surface of the mold wall. It has long been common practice in the centrifugal casting industry to rebore molds from time to time in order to remove the damaged inner surface. The extent to which the reboring 4 Claims. 29-1482) operations can be carried is limited, however, by

squeezing process. In this process the used mold is placed upon a cylindrical mandrel having a diameter slightly less than the-inner diameter of the mold, the difference in diameter determining the extent to which the mold is to be contracted or shrunk. The mandrel and mold are then placed in the bore of a container for high pressure fluid, the outer surface of the mold being spaced from the wall of the container to such an extent as to enable a fluid under pressure to be admitted to the space thus provided. The ends of this space being suitably sealed'to confine the fluid therein, when fluid is introduced into the space and subjected to sufficient pressure the mold may be con process is not so well adapted to molds of large tent.

2 diameter, nor is it well adapted to any considerable reduction of the mold diameter.

In endeavoring to find a process whereby used molds of large diameter could be reclaimed, as

. well as a procedure for efiecting a greater reduction in diameterthan has heretofore been practicable, I have made various experiments with a procedure whereby a longitudinal strip is removed from the wall of a cylindrical mold so that the edges of the slot thus formed can be brought together and welded, Of course this procedure serves to reduce the diameter of the mold, so that the smaller mold thus formed may be rebored to remove the damaged inner surface and produce a reclaimed mold having an inner diameter substantially the same as the inner diameter of the mold when originally made.

In 'the course of these experiments I have discovered that there are present in a used mold inherent contractile stresses of such magnitude as to be capable of contracting the mold circumferentially to a substantial extent when a longitudinal strip is removed from the mold wall, and that the procedure may therefore be regarded as a stress-relieving operation. I- have also found that the circumferential contraction of the mold due to these contractile stresses in the mold wall operates to close to a substantial extent .thelongitudinal fissures in the inner surface of the mold wall. It has also been found that when the inherent contractile stresses in the mold are insufficient to close completely the slot produced by the removal of the longitudinal strip from the mold wall, extraneous force may be applied to the mold to bring the edges of the slot into abutting relation and to restore the cylindrical shape ofthe mold, so that the abutting edges may be welded to produce a reclaimed mold within the required tolerances as to diameter and shape. The use of extraneous force to close the slot also serves to close the longitudinal fissures in the inner surface of the mold wall to a further ex- This partial closure of the longitudinal fissures has been clearly observed in the reboring operations, the fissures being found completely closed at a depth which is less than their original depth before the removal of the longitudinal.

strip.

As will be apparent from the above, the main purpose of the present improvement is to reclaim cylindrical metal molds which have been used to such an extent in casting pipe and the like centrifugally that the inner surface of the mold wall is so roughened, checked and uneven that satis factory castings can no longer be made therein or removed therefrom, or which have been used to such an extent that the inner diameter has been 50 increased by repeated reboring or grinding that castings of the desired diameter and wall thickness can no longer be made therein. It is also an object of the invention to relieve such a used mold oi the inherent contractile stresses developed therein during use. Another object of the improvement is a method of closing the iongitudinal fissures or checks formed in the inner surface of the mold as a result of the alternating high and low temperatures to which the mold is subjected. A further object of the invention is an improvement in the procedure for reducing the inner diameter of a. centrifugal mold while retaining the desired wall thickness. A still further object is the provision of a method whereby the inherent contractile stresses in a used mold may be utilized in effecting a reduction in the diameter of the mold.

In accordance with the present invention. the above objects are accomplished by cutting a longitudinal strip from the wall of the used mold, bringing into abutting relation the edges of the slot thus formed, applying to the outer surface of the mold such controlled pressures as may be necessary at various points to bring the mold into round, welding the abutting edges of the slot together, and finally removing, by a boring operation or the like, as much of the damaged inner surface as may be necessary to provide a suitable casting surface. In some cases the inherent contractile stresses in the used mold will be suflicient to bring the edges of the slot together. When the inherent stresses are incapable of bringing these edges together, as where a considerable reduction in diameter of the mold is desired and a relatively wide strip is removed, extraneous pressure on the outer surface of the mold, preferably at spaced points along each edge of the slot, is utilized for bringing the edges together and holding them in this position during the welding operation. Such extraneous pressure is also utilized for restoring the cylindrical shape of the mold in case the mold tends to be out of round when the edges of the slot are brought into abutting relation.

In order that the invention may be better understood, reference is hereby made to the accompanying diagrammatic drawing wherein:

Fig. 1 is a plan view of a well known form of centrifugal mold to which the present improvement is adapted, portions thereof being broken away to show the complete structure;

Fig. 2 is a plan view similar to Fig. 1. but with the bell and ring carrier removed;

Fig. 3 is a view of the ring carrier removed from the cylindrical portion of the mold and partly broken away;

Fig. 4 is a plan view of the bell end of the mold removed from the cylindrical portion and partly broken away;

Fig. 5 is a plan view showing the cylindrical portion of the mold with a longitudinal strip removed therefrom and the edges of the slot prepared for welding;

Fig. 6 is an end view of the cylindrical portion shown in Fig. 5, and illustrating the shape of the edges of the slot after these edges have been prepared for welding;

Fig. 7 is a diagrammatic plan view showing the preferred manner in which extraneous pressure is applied at various points along the edges of the slot in the mold in order to bring the edges into abutting relation and restore the cylindrical shape of the mold;

Fig. 815 a sectional view taken on the line 88 of Fig. 7 and showing in more detail the preferred procedure oi applying extraneous pressure to the mold; and

Fig. 9 is a detailed, cross-sectional view of the completed weld.

The type of centrifugal mold shown in the drawing for the purpose of illustrating the improved process is well known in the industry and comprises a main cylindrical portion [0 having an enlargement in the form of a bell ll integral with one end thereof and another enlargement constituting a ring carrier i2 welded or otherwise formed on its opposite end. The ring carrier I2 is usually formed with an internal flange IS the inner edge of which is fitted upon the end of the cylindrical part of the mold and welded thereto. In practicing the present process the ring carrier I2 is removed by cutting through the flange I3 aroundthe circumference of the cylindrical portion i0 and on a line indicated by the arrow a in Fig. 1. The bell end II, or a part thereof, is also removed by a circumferential cutting operation at one or the other of the points indicated by the arrows b and c in Fig. 1. When the entire bell portion of the mold i cut away and the ring carrier I2 is removed,

the mold proper, or the cylindrical portion I0.

will appear as illustrated in Fig. 2 of the drawing.

Following the removal of the end portions of the mold in the manner described above, a longitudinal strip is cut out of the mold wall by the use of a lathe or cutting torch. The edges of the slot thus formed, and shown in Figs. 5 and 6, are machined so that they may be prepared for the subsequent welding operation. The strip which is removed from the mold wall will vary in width in accordance with the diameter of the mold and the extent to which the diameter is to be reduced. With a twelve inch mold. for example. the width of the strip may vary from one and one-half inches to two inches. In any case, it is desirable to machine the edges of the resulting slot so that these edges may be of such a shape as to produce a welded joint of the character desired. A preferred form of Joint is one in which the edges of the slot are machined away as indicated at 14 in Figs. 5 and 6 so that a U- shaped welding groove l5 will be formed when the projecting edges I8 are brought into abutting relation as illustrated in Figs. '7, 8 and 9.

In some cases the inherent contractile stresses in the used mold are sufficient in magnitude to bring the opposite edges of the slot together when the longitudinal strip is removed from the mold wall. In such cases it is necessary to provide some means for preventing the mold from contracting during the removal of the strip and while the edges of the slot thus formed are being machined or otherwise suitably prepared for the welding operation. Any suitable pressure applying means operating within the bore of the mold may be used for this purpose.

When these contractile stresses are not suflioient to bring the edges of the slot together, as in those cases where it is desired to effect a maximum reduction in the diameter of the mold by the removal of a strip of considerable width, the application of extraneous forces to the outer surface of the mold is resorted to for the purpose of bringing the edges l8 into abutting relation. The manner in which such forces are applied is c the drawing. As shown therein, the mold is supported upon a suitable base ll arranged opposite the longitudinal slot and extending throughoutthe length of the mold, and pressure is applied at various points ll along each edge of the slot in a direction approximately toward the axis of the mold. This pressure may be applied through a system of levers It. i'ulcrumed at the points indicated at 2|, and having their inner ends contacting. with the outer surface of the mold at the points It adjacent the edge of the slot. Upward pressure at points it on the outer ends of the levers It, as by means of a series of independently operated hydraulic jacks. makes possible the application of the desired amount of pressure at each of the points. where the inner ends of the levers bear upon the outer surface of the mold. In this manner the pressure at the various points i8 maybesoregulatedastobringtheedges it into exact alignment and abutting relation, and

then regulated so as to restore the cylindrical shape of the mold, that is. bring it into round at all points throughout its length. A similar procedure may also be followed in restoring the cylindrical shape of the mold where the inherent contractile stresses alone are utilized for closin the longitudinal slot.

When the edges II have thus been brought into alignment and into abutting relation, and the cylindrical form of the mold has been restored, the joint is completed by a suitable welding operation. In practice it ispreferable to provide sufllcient space between the inner ends of oppositely arranged levers it so that the welding operation can be performed without interference by the pressure applying means. Notwithstanding the enormous force required to bring the edges of the slot together and to restore the cylindrical shape of the mold, the cylindrical shape is maintained after the welding operation has been completed and the application of extraneous pressure has been discontinued. 1

After the edges of the slot have been welded together and the pressure on the outer surface of the mold has'been discontinued, the ring carrier l2 and the bell II are rewelded to the cylindrical portion ill. Inasmuch as the cylindrical portion has been reduced in diameter, it is necessary to build up the inner edge of the flange I3 by a welding operation before the ring carrier can be welded in place. The inner edge of the rebuilt fiange l3 and the outer surface 22 of the spigot end of the mold are then machined to fit, after which the ring carrier is welded in place. The hell i I may be welded to the opposite end of the cylindrical portion by any suitable form of joint and welding operation. As the cylindrical portion has been reduced in diameter, the inner surface of the bell may be built up thereafter by a welding operation to such extent as may he desired to bring it into conformity with the cylindrical portion Hi.

The reclaiming operation is then completed by reboring the inner surface of the mold to such a depth as may be necessary to remove the damaged portion of the wall and provide a new casting surface. A rough machine cut is preferably taken on the outer surface of the mold in order to insure that the mold wall may be'of uniform thickness. The condition of the welded longitudinal Joint upon its completion and after the mold has been rebored, and also machined on the outside, is illustrated at 23 in Fig. 9 of the drawing.

serve in this manner to partially close the lon itudinal fissures in the surface of the mold bore. Likewise the application of extraneous pressure to the outer surface of the mold. at various points along the opposite edges of the slot, operates to close these fissures to a still further extent. In-

asmuch as these fissures are substantially of I V-shape in cross section, when they are thus partially closed it is not necessary to machine away as much material to renew the casting surface as would he required if the fissures remained open to their original depth, This effect is in noticeable contrast to the behavior of such fissures in the mold reclaiming processes heretofore employed, where the tendency of the fissures is to remain entirely open.

While the present improvement has been described in detail above in connection with a procedure in which the entire bell end of the mold is removed on a circumferential line indicated by the arrow 1) in Fig. 1, it will be understood that the procedure is equally applicable when a portion only of the bell end of the mold is removed, such. as the core seat and ring gear flange, on a line indicated by the arrow c in Fig. 1. It will also be understood that the improvement may be utilized in reclaiming any desired portion of the cylindrical part of the mold disclosed herein, and in reclaiming moldsof a type V and shape different from that disclosed. The invention is therefore' not intended to be limited to the specific procedure which has been shown and described, and it is to be understood that it is subject to such variations as come within the scope of the appended claims.

What I desire to claim is:

1. The method of reclaiming a cylindricalmetal mold employed for centrifugally casting pipe and the like and having therein contractile stresses resulting from use in casting, which comprises removing a longitudinal strip from the wall of the mold whereby said contractile stresses operate to contract said mold circumferentially and thereby bring into abutting relation the edges of the slot thus formed, and welding said edges together.

2. The method of reclaiming a cylindrical metal mold employed for centrifugally casting pipe and the like and having therein contractile stresses resulting from use in casting. which comprises removing a longitudinal strip from the wall of the mold whereby said contractile stresses operate to contract the mold circumferentially and thereby reduce the width of the slot thus formed, applying pressure to said mold to brin the edges of said slot into abutting relation, and welding said edges together.

3. The method of reclaiming a cylindrical metal mold employed for centrifugally casting pipe and the like and having therein contractile stresses resulting from use in casting, which comprises removing a longitudinal strip from the wall of the mold whereby said contractile stresses operate to contract said mold circumferentially and thereby reduce the width of the slot thus formed and close to a substantial extent the iongitudinal fissures in the inner face of the mold, applying extraneous pressures to the outer face of the mold to close said slot and to further close said fissures, varying said pressures upon diner- 7 eat regions or the mold to restore the cylindrical shape or the mold; and welding the edges o1 adjacent the edges oi said slot to Zoroe sold edges into abutting relation and to further close the drical portion, applying extraneous pressures '35 themes, will said pressure: to restore the cylindrical shape of said cylindrical portion. weldinz sold edges together. and welding a bell portion on' the relomed cylindrical portion.

CIIEFORD R. TINBLE'Y.

REFERENCES CITED The following references are of x'ecord in tEe file of this potent:

UNITE EZATEE PATENTS Number Name Date 1,71%,720 Martin ei; e3. June 3.8, 1929 1,722,671 Lingo July 30, 1929 1,856,874 Lengenberg May 3, 8932 1,934,822 Sawyer Nov. 14, 1933 2,287,@33 Eerkling Dec. 23, 1941 2,268,843 Phillipe Dec, 30, 1941 

